This project investigates the environmental and physiological regulation of the pineal gland, exclusive of transmembrane and intracellular regulatory mechanisms (See Z01-HD 00095-17 LDN). The pineal gland is part of the melatonin rhythm generating system, a neural circuit which includes a circadian clock in the suprachiasmatic nucleus (SCN); the SCN is reset and entrained by light acting through the eye. It has been proposed that the SCN pineal circuit passes through the paraventricular nucleus of the hypothalamus (PVN). This past year work was completed which supports this with the demonstration that electrical stimulation of PVN stimulated the production of melatonin at a near physiological rate. In other studies, the photoneural regulation of pineal rhodopsin kinase and phospholipase C have been studied; and the developmental appearance of both phospholipase C and Na+/K+-ATPase has been examined. It has been discovered that Na+/K+-ATPase develops after birth, as indicated by both ouabain binding and two indices of enzyme activity, ATP hydrolysis by membrane preparations and uptake of rubidium. Results indicate a high affinity form of Na+, K+-ATPase, similar to the a+ form which has been described in the brain, is the dominant form present in the pineal gland. This indicates that another mechanism might generate membrane potential before this time.